Speech suppression by predictive filtering

Claim 2

Speech processing apparatus for suppressing voiced segments of an undesired speech signal while leaving a desired speech signal intelligible, comprising: means for deriving an electronic waveform representing the undesired speech signal; means for deriving an electronic waveform representing a composite signal containing a reverberant version of the undesired speech signal and the desired signal; means for deriving from the waveform of said undesired speech signal a delay parameter determined from the signal values during an interval embracing a substantial portion of a pitch period of said undesired speech signal; means for applying said composite speech signal waveform to a summer over a first path; means for delaying in a second path said composite speech signal waveform by an amount of said delay parameter; and means for subtractively applying to said summer the delayed said composite speech waveform.

Claim 3

Apparatus pursuant to claim 1, further comprising means responsive to the absence of voiced segments of said undesired speech signal for interrupting said second path.

Claim 4

Apparatus in accordance with claim 1 further comprising means for deriving from the waveform of said undesired speech signal a gain parameter specifying the amount by which the amplitudes of corresponding values of said undesired speech signal in a past said interval must be respectively adjusted so as to produce a substantial duplicate of the undesired said speech signal of a present said interval; and which further comprises means controlled by said gain parameter for amplifying said delayed composite speech waveform prior to its being subtractively applied to said summer.

Claim 5

A communications network comprising: a hands-free telephone station including a direct acoustic coupling path between the station loudspeaker and microphone, a second remote telephone station, and transmission means interconnecting said stations; means for deriving-from the incoming signal waveform to said loudspeaker from said second station-a delay parameter representing the duration of an interval embracing a substantial portion of the present pitch period of speech from the remote station; and a gain parameter specifying the amount by which the waveform in a past said interval must be changed in amplitude to substantially correspond to the undesired speech waveform of the present interval; means for applying the composite signal-consisting of the desired near-end talker signal and the acoustically coupled far-end talker signal from said loudspeaker-in said microphone output to a summer over a first path; means disposed in a second path for delaying said composite signal by the amount of said delay parameter and for amplifying the delayed composite signal an amount determined by said gain parameter; and means for subtractively applying the delayed, amplified composite signal to said summer.

Claim 6

A communications network comprising: a hands-free telephone station including a direct acoustic coupling path between the station loudspeaker and microphone, a second remote telephone station, and transmission means interconnecting said stations; means for deriving-from the incoming signal waveform to said loudspeaker from said second station-a delay parameter representing the duration of an interval embracing a substantial portion of the present pitch period of speech from the remote station; and a gain parameter specifying the amount by which the waveform in a past said interval must be changed in amplitude to substantially correspond to the undesired speech waveform of the present interval; means for applying the composite signal-consisting of the desired near-end talker signal and the acoustically coupled far-end talker signal from said loudspeaker-in said microphone output to a summer over a first path; means disposed in a second path for delaying said composite signal by the amount of said delay parameter and for amplifying the delayed composite signal an amount determined by said gain parameter; and means for subtractively applying the delayed, amplified composite signal to said summer.

Claim 7

A communications network pursuant to claim 4 wherein said deriving means comprises: a signal sampler connected to the circuit of said loudspeaker and operating at a set sampling rate; and means for computing values of a term Xj in accordance with the relationship

Claim 8

A communications network pursuant to claim 5 wherein said gain parameter deriving means comprises means for computing the value b in accordance with the relationship

Claim 9

A communications network pursuant to claim 6, further comprising means for rendering said gain parameter equal to zero in the absence of voiced segments of the signal in said loudspeaker path from said remote station.

Claim 10

A communications network pursuant to claim 7, further comprising means for setting said gain parameter equal to zero in response to values of Xk, corresponding to the maximum computed values of Xj which are less than a critical predetermined value.

Claim 11

A communications network pursuant to claim 8, further comprising means for adjustably delaying arrival of said delay and gain parameters at said second path by an amount that compensates for the transit time delay over said direct acoustic coupling path of speech from said remote station.

Claim 12

A communications network pursuant to claim 4, further comprising: filter bank means connected to the output of said summer and comprising plural contiguous subbands; means for producing-from said remote station speech signal-control signals representative of the incoming speech energy level in each said subband; means for center-clipping the output of each said filter bank subband a varying amOunt in response to the concurrent said energy level value; and means connecting said control signal producing means and said deriving means responsive to voiced portions of signal from said remote station for reducing all said clipping levels.

Claim 13

Speech processing apparatus for suppressing speech from one of two talkers in a room comprising: first and second microphones located equidistant from the first, desired said talker but at unequal distances from the second, undesired said talker; means for deriving from the two said microphone outputs a first parameter Xj in accordance with the relationship

Claim 14

Speech processing apparatus for suppressing speech from one of two talkers in a room comprising: first and second microphones located equidistant from the first, desired said talker but at unequal distances from the second, undesired said talker; means for deriving from the two said microphone outputs a first parameter Xj in accordance with the relationship